Mechanical presses which punch metal plate have been in use for many years. In the trophy manufacturing business, for example, such presses produce insert discs for decorative plaque holders. Generally, these discs are round and the most commonly used sizes are 7/8, 11/4 and 2 inches in diameter. Most of these insert discs are produced from lengths of thin sheet metal, such as aluminum, on which graphic art work is photo-etch engraved in series along the length of the strip. The art work pattern is generally round and slightly smaller in diameter than the disc size that is to be produced. The discs are then stamped out along the strip and then inserted into the decorative blank holder and held in place by a conventional adhesive material or process.
In this industry, for esthetic and safety reasons, it is important that the rough edge or "burr-side" that is caused by fracturing during the blanking operation be on the side of the sheet opposite that on which the art work resides. It is also important that the blank outside diameter be concentric, in the case of circular blanks, with the periphery of the circular engraved pattern, and that the engraved surface be free of scratches.
In the past, blanking operation has been accomplished by using conventional punch presses, the punch of which pierces the photoetched sheet in the conventional manner from the top, and passes down into a matching die located below the workpiece.
In order to produce the fracture burr on the side opposite the engraved or finished face side, the material is stamped with the engraved or face side down. A pilot system is normally used to try to blank the strip in the proper places. In this method, a first part is carefully blanked out as concentric with the design as possible by using mirrors or viewing from below, for example, and thereafter, each consecutive blank is processed by moving the strip an amount equal to the center-to-center distance between the successive individual art work designs.
The problem with this technique is that it requires much skill to obtain the first or pilot blank is exactly the right spot. Any error in centering here will be transmitted to all successive blanks. Also, this method requires that the design be exact progression on the strip, for if they vary, the blank outside diameter will no longer be concentric with the design. Further, by requiring that the art work be on the bottom of the strip being blanked, the design is often scratched as it slides along the die.
Still another method that is currently is use to accomplish this type of blanking operation is the use of a conventional punch press with a conventional die secured to the platen and having a prism or optical mirror positioned directly below the die opening, thus allowing the operator to see up into the die cavity in order to center the engraving concentrically within the die before tripping the press. Again, there is here the disadvantage of scratching the design because the art work is on the under side of the strip. In this configuration, the mirror often becomes soiled from parts dropping on it and from oil and grime adhering on the mirror's surface, so that it becomes increasingly more difficult to properly operate the machine. Further, the operator will not be able to look where her or his hands are, which creates an unsafe condition.
Three prior art press of which the inventor is aware are hereinafter described. U.S. Pat. No. 1,999,730 describes a blanking press which provides a blank of sheet material and thereafter draws or presses the blank into a desired hemispherical shape. The sheet material from which the blank is stamped is preferably previously printed in simulation of the iris and upper lid of a dolls eye. In this machine, as the upper die portion descends, the punch cuts a blank from a strip, and forces this blank against a forming post.
In U.S. Pat. No. 2,772,735, a single action multiple slide press having cooperative punching and cutting dies is shown. As the sliding head of the press is lowered, a centering ring engages an upper end of a neck portion of a preformed blank and centers it so that further downward movement of the head will move the blank telescopingly onto a cutting punch and into engagement with a punch supporting member.
Finally, U.S. Pat. No. 3,336,117 describes a two-member punch die which is used in the producton of finished expanded metal blanks. The upper die member or punch holder includes a body having a machined main cavity therein which slidably receives a spring-loaded cup forming punch and a cup wall crushing punch. The lower die has a body similarly provided with a main cavity in which a spring-loaded pad and stripper member is slidably disposed. The die members are mounted for movement in a conventional die press where the upper member is moved downwardly to cause a shearing action on a supply strip by cooperating cutting edges. Continued downward movement of the upper die member about the lower die member causes a sliding movement of a stripping member within a die cavity until the work-in-progress blank is pushed into a smaller diameter counter bore to form a cup or annular peripheral section on the blank about a forming head. At the end of the cycle, the punch holder is removed from about the die member and the finished blank is ejected by the return of the stripping member.
In all of the above-described presses, the punch portion of the press is moved downwardly, causing a shearing and/or forming process to occur. There is no facility in any of these machines for unobstructed visual observation by the machine operator of the actual work area in order to allow proper alignment of a design within the die perimeter. It should therefore be evident that a blanking press which allows the press operator to look down on the press to move a workstrip so that artwork designs may easily and accurately be centered with respect to the periphery of the die opening, would constitute a significant advancement in the art.